1. Field of the Invention
The present invention generally relates to cardiac pacing systems and, in particular, to methods and medical systems for determining a link quality and a link quality margin of a communication link between a programmer device and an implantable medical device of such a medical system.
2. Description of the Prior Art
Telemetry communication is normally used between an implantable medical device, such as an implantable bi-ventricular pacemaker or a CRT (Cardiac Resynchronization Therapy) device, and an external or programmer workstation to transfer data between the devices, for example, to transfer IEGM data of the heart of the patient from an implanted device to the programmer or to transfer updating data for updating a certain setting of the implanted device from the programmer to the implanted device. In telemetry communications, the operation depends inter alia on used transmission power, interference, reflecting properties in the near environment, the placement of the RF communication unit of the programmer etc. A user of the programmer device and/or the pacemaker needs information of the telemetry performance during such a telemetry communication session, for example, in order to be able to place the RF communication unit at a good position. If the RF communication unit is placed at a bad position, the radio link will be unreliable and it might even break down. Today, the link quality is used to judge whether the RF communication unit is placed at a suitable location with respect to the patient carrying the implanted medical device. The link quality is affected by the separation between the RF communication unit and the implanted medical device and the interference, which may arise from external functions (i.e. external device in the environment) but also from device internal functions (e.g. high voltage charge or shocking). Thus, there would be an advantage if the user of the programmer and/or the implantable medical device were provided with an indication of the link quality.
In U.S. Pat. No. 6,647,299, a solution where a light emitting diode (LED) is used as visible indicator to assist a user to find the desired telemetry location of a programmer for a bi-directional communication link between the programmer and an implantable medical device. Through variations of the visible indicator, the user will know the relative location of the programmer and the implanted device. When the programmer is in the proper telemetry position and the signal strength and accuracy have been confirmed, the light indicator will indicate that a link has been established.
However, a problem with existing link quality indicators is that they are based on the momentary conditions and do not identify whether there is a sufficient link quality margin to cope with a sudden increase in the level of interference. In U.S. Pat. No. 5,843,139 various aspects of system performance in a system including an implantable medical device and a programmer are monitored to determine the momentary performance of the system. The monitored parameters comprises bit-error rate, signal strength, signal-to-noise ratio and the presence of local RF noise and non-telemetry RF-signals.
Therefore, it would be advantageous if a link quality and/or a link quality margin of a communication link between a programmer and an implantable medical device could be continuously monitored during a communication session.
Furthermore, there is a need within the art of an efficient, reliable and simple way of testing the link quality and/or link quality margin of a communication link during a communication session between an implantable medical device, such as a pacemaker, and an external device, such as a programmer workstation.
It is also desirable to provide means for presenting the link quality or the link quality margin for a user, such as a physician, of the programmer device or for a patient in a distinct and intuitive manner.